The field of the invention is disconnect switches, and more particularly, manually operated disconnect switches having a set of movable contact blades which are pivoted by rotating a crossbar between an opened and closed position.
As illustrated in U.S. Pat. No. 1,918,248, the crossbar which carries the movable contact blades is rotatably mounted to an insulating block that is typically mounted inside a cabinet and the crossbar is coupled to a handle mounted on the exterior of the cabinet through a spring loaded trip mechanism. The handle and associated trip mechanism may be mounted to one side of the disconnect switch, or as shown in U.S. Pat. No. 3,602,676, the handle may be mounted to the front of the cabinet and its trip mechanism coupled to a point intermediate the ends of the crossbar.
When in their closed position, the movable contact blades electrically connect with a set of stationary contacts to conduct electric current from a set of input terminals to a set of output terminals. As illustrated in the above cited U.S. Pat. No. 3,602,676, each movable contact blade is typically connected to an output terminal through a flexible conductive strap, or pigtail, that allows the movable contact blade to be freely pivoted between its opened and closed positions.
As illustrated in U.S. Pat. No. 3,684,849, the current carrying capacity of disconnect switches is often enhanced by employing arc chutes. Such arc chutes are comprised of a series of metallic deionization plates which are mounted to the insulating block and positioned directly above each movable contact blade. Arcs which may result when the disconnect switch is opened are cooled and eventually extinguished by the deionization plates in each arc chute.
Disconnect switches are often employed with other electrical components to form control circuits such as motor starters. In such control circuits the disconnect switch serves not only to control the main electrical power through the operation of its movable contact blades, but also, to control the operation of other elements in the control circuit through the operation of auxiliary contacts which are mounted to the insulating block. The number and nature of such auxiliary contacts vary with each particular application of the disconnect switch and, therefore, these are typically fastened to the insulating block at any point which allows them to be mechanically coupled to the rotatable crossbar.
Prior disconnect switches are difficult to maintain and service. For example, if a movable contact blade is to be replaced, the arc chute located directly above it must be removed and the flexible strap which connects it with the output terminal must be unfastened before the blade can be detached from the crossbar. Although some prior art structures allow the arc chutes to be removed and replaced as an integral unit, the fastening devices which hold such arc chutes to insulating blocks are often accessible only by removing the insulating block from its enclosure. Also, although prior auxiliary contacts are typically enclosed in self-contained cartridges, these cartridges are mounted to the front or side of the insulating block using fastening means which may not be easily accessible when the disconnect switch is mounted within its enclosure.